The invention relates to venetian type blinds and particularly to the drum inside the headrail to which a ladder that carries the slats in a venetian blind is attached.
Venetian type blinds have a series of slats hung on ladders that extend from a headrail to a bottomrail. The slats rest on rungs between rails of the ladders. The number of ladders will vary according to the width of the blind. However, all venetian blinds have at least two ladders. In most venetian blinds the upper end of each ladder is attached to a drum. The drums are carried on a tilt axle within the headrail. The tilt axle is connected to a tilt mechanism that enables the tilt axle to be turned in a clockwise direction as well as in a counterclockwise direction. The blind is in an open position when the rungs are horizontal. To close the blind one turns the tilt axle in either a clockwise direction or a counterclockwise direction. This turns the drums on the tilt axle lifting one rail while allowing the other rail to be lowered thereby raising one end and lowering the opposite end of each rung tilting the slats. Turning the tilt axle and attached drums in an opposite direction opens the blind. The rails originally used for ladders in venetian blinds consisted of a fabric tape typically from one to two inches in width. The rungs were also made of fabric strips. Very few tape type ladders are used in blinds today. Rather, the art has adopted ladders formed of cord rails having cord-type rungs between them. Typically, the rungs are multiple strands of cord. However, a single strand of cord has also been used. Frequently, a braided cord is used for the ladder rails.
In most Venetian type blinds the drums that hold the rails of the ladders are circular or nearly circular. Consequently, when such a drum turns, the upper portion of the rails of the ladder cannot move together when the blind is changed from an open position to a closed position. That is so because all diameters of the tape drum are the same or nearly the same. Because the rails cannot move together at the top of the blind the upper slat does not close tightly allowing more light to pass through the blind at the location of the top slat than would pass if the ladders had moved together. This problem can be overcome by using a tilt system in which the upper portion of the rails move together. Such a tilt system has been disclosed by Judkins in U.S. Pat. No. 5,573,051. The tilt mechanism disclosed by Judkins has a disk to which the rails of the tilt ladder are connected. There is one disk for each tilt ladder. The disks are mounted on a tilt rod so that rotation of the tilt rod will turn the disks in unison. This tilt mechanism requires special hardware and requires routing the lift cords through the disks. It cannot be easily retrofitted into existing headrails. Furthermore, the tilt mechanism disclosed by Judkins ca only be used for cord type ladders.
There is a need for a drum that supports the rails of a ladder in a venetian type blind and allows the ladder rails to move together at the top of the blind when the blind is closed. This drum should be easy to install, able to handle both cord ladders and tape ladders and be suitable for use on existing blinds. Such a tape drum should also be inexpensive and easy to make.
I provide a tape drum for a venetian type blind that has two elongated ends that are generally elliptical or oval in shape. The major diameter preferably is about twice the minor diameter. There is a front wall and a rear wall extending between the two ends. A rib extends inward from each of the front side and the rear side. These two inwardly extending ribs are in a common plane but are spaced apart. A bracket or mounting is attached to each wall, the brackets being sized and configured so that a cord rail can be easily attached to it. A pair of spaced apart rods extend inward from the inside surface of each elongated end. The rods are positioned so that there are two pairs of rods in which the rods in each pair are collinear but are spaced apart from one another. These rods provide a mounting for tape ladders and are sized for attachment of a tape rail to each collinear pair of rods. A hole is provided in each elongated end to permit the drum to be slid onto a tilt axle. The holes are the same shape as the cross-section of the tilt axle. When the tilt mechanism closes the blind the rails of the ladder move together throughout the length of the ladder and particularly in the region of the top slat.
Although the preferred embodiment has mountings for both tape ladder rails and cord ladder rails, the drum could be made with either but not both type of mountings.
Other objects and advantages of the present invention will become apparent from a description of the present preferred embodiments shown in the drawings.